Multiple geochronological evidences revealing oil charging and redistribution processes in the Tazhong-4 Oilfield, Tazhong Uplift (Tarim Basin): Implications for quantitative reconstruction of petroleum accumulation history in superimposed basins

Abstract

Re-migration within a hydrocarbon reservoir is an important yet poorly constraint process in petroleum system analysis. Here we investigated a Paleozoic petroleum reservoir in the Tarim Basin and quantitatively reconstructed the oil re-migration process using fluid inclusions and multiple isotopic dating techniques including the calcite U–Pb dating, the oil Re–Os dating, and the illite K–Ar dating. The Re–Os dating for the Carboniferous oil samples demonstrated an oil generation process during the Middle Caledonian (479 ± 110Ma). Two episodes of oil charging were revealed by each represented oil inclusion fluorescing yellowish and blue color in the Cambrian and Ordovician intervals. Calcite U–Pb ages suggest the Cambrian and Ordovician paleo-reservoirs represented oil inclusion fluorescing yellowish color were charged by mature oils during the late Caledonian orogeny (420-384Ma), and illite K–Ar ages show the oils with similar maturity charged into the Carboniferous reservoir during the late Hercynian orogeny (278.4–246.0Ma). This contradiction in absolute ages reveals an oil re-migration process with oils that originally was generated during the Middle Caledonian and charged in the Cambrian and Ordovician reservoirs and then migrated vertically to the Carboniferous reservoir ∼200 Myrs later possibly due to fault reactivation. The successful application of fluid inclusion analysis and multiple absolute dating techniques in the Tarim Basin provides a paradigm for quantitative reconstruction of petroleum (re-) accumulation history in similar tectonic superimposed basins.